It is known that crystallized slags from iron- and steel-making and the metallurgy of nonferrous metals must after cooling, undergo either a dimension reduction operation by crushing if the material is to be obtained in pieces, or by grinding to a greater or lesser degree if the material is to be reduced to a fine powder. These crushing and/or grinding operations involve high energy consumption per ton of material treated and very substantial equipment outlays and maintenance costs due to the rapid wear of the active elements of the machines.
In order to improve the crushability and/or fine grindability of the slags after cooling, it has been recommended that there be injected into the molten slags and cinders, while they are being poured from the ladle, products with a fine particle size capable of generating gases which remain imprisoned in the slag particles and give rise to cellular or alveolar materials. For this purpose one may cite: carbon black, coke fines, or, better still, compounds such as alkaline earth carbonates, such as limestone, for example, which, upon thermal dissociation, cause an endothermal reaction with the molten slag and which, after decomposition, provide slag enriching elements (See U.S. Pat. No. 4,062,672).
It has now been found that slags can be expanded and at the same time their physical and/or chemical characteristics can be modified at will while maximizing the use of the sensible heat of the molten mass at the time it leaves steel mill or blast furnace converters, by injecting specially adapted porophoric mixtures based on at least two components.
According to the principal objective of the present invention, these mixtures are composed, on the one hand, of carbonated materials and, on the other hand, of materials with a free carbon. These materials can be natural or manufactured materials. However, it has been found particularly advantageous, in the mixtures according to the present invention, to use by-products which are presently considered to be wastes and residues and are dumped unchanged on the slag heap.